Insights in Public Health

On October 22, 2015, the Hawai‘i District Health Office (HDHO) was notified by the Disease Outbreak Control Division (DOCD) of a confirmed dengue case with no travel history; this was the first locally transmitted dengue case of the 2015 Big Island outbreak. The HDHO's response team, composed of four Vector Control and 10 Sanitation staff, was minimal. Immediate vector response efforts, to reduce or eliminate transmission risk, included field spraying to control adult mosquitos, larvaciding and mosquito breeding source reduction, and public education outreach activities within a 200-yard radius around the case's property. Initial efforts were not successful in containing further dengue cases.

By the end of November 2015, the Department of Health had confirmed 112 dengue cases, with the HDHO response team working seven days a week spraying a total of 195 properties and conducting mosquito surveys on more than 1,000 properties. It was evident early in the outbreak the initial 14 staff could not sustain the rigorous response demands; additional resources from across the state were requested. An estimated 30 Department of Health individuals from neighbor island Vector Control, Sanitation, and Indoor Radiological Health programs were enlisted. Additionally, an estimated 30 staff, including from HDHO Public Health Nursing, HDHO administrative office, and the County of Hawai‘i, participated in the response.

The Hawai‘i Island Dengue outbreak lasted seven months with 264 confirmed cases of dengue recorded, 879 properties sprayed, and more than 5,000 properties surveyed. The dengue outbreak was a stressful and daunting experience for the response teams and communities as well as the victims themselves.

Following the outbreak, HDHO self-assessment along with the US Centers for Disease Control and Prevention's (CDC) assessment of the response afforded opportunity to identify shortcomings and improve vector program operations to improve future response. To date the program has focused efforts in three main areas: preparation, prevention, and response.

Preparation

Both HDHO and CDC assessment processes concluded a lack of trained vector control staff severely limited capacity to respond to arboviral (viruses transmitted by arthropod vectors) outbreaks.¹ The inadequacy also prevented routine work in areas of mosquito surveillance, mapping, monitoring for resistance, and mosquito suppression, key components of an integrated approach to mosquito management.² This program deficiency is directly attributed to the 2008 reduction in workforce that resulted in terminating 10 of 14 positions including vector inspectors, workers, a laboratory assistant, and an entomologist. A tremendous effort to restore the Vector Control program was undertaken with the legislature and administration creating a total of 30 new positions statewide since the 2015 outbreak. Ten were allocated to Hawai‘i Island, increasing the current HDHO Vector Control program in that area to 14 positions.

Staff training is an essential component of program preparedness and has been a major area of emphasis following the outbreak. Training sessions have included day-long classroom sessions, field exercises, mock responses, as well as a two-and-one-half day statewide conference where specialists from Hawai‘i and the mainland presented topics related to mosquito management and response strategies for arbovirus introductions.

All staff personnel have received training on the safe and proper use of the pesticidal abatement products and the various types of equipment used by the program, and were certified as pesticide applicators for public health pest control. Such training and certification ensures chemical interventions will have the least possible nontarget impacts, be in full compliance with applicable laws, and be safe for residents within treated areas. Staff knowledge and understanding of the modes of action of chemicals employed prepares them to discuss with and ensure risks are aptly conveyed to residents, who are often fearful of pesticides, the nature of the products, and equipment in use.

Staff personnel have also received extensive training in the biology of Hawaii's various vector organisms, habitats, and environments in which vectors thrive; the biology of disease organisms with elevated potential to enter the islands; and nuances of interactions between the vector and the disease it may carry. Not only is such knowledge important for on-site risk assessment and treatment considerations, but it is also important for educational outreach aspects of Vector Control program activities.

The final major limitation identified as related to preparedness was a lack of equipment and supplies to respond to emergencies or even conduct routine surveillance and laboratory activities. The Vector Control program accessed state emergency funds and a CDC Epidemiology and Laboratory Capacity for Infectious Diseases grant to purchase vehicles, pesticide products, various types of application equipment, water transporting containers, safety equipment, a droplet calibration device, microscopes, insect rearing supplies, surveillance traps, trap batteries, and field assay kits for testing mosquitoes for disease. The field kits are not definitive but only serve as a tool to assess disease risk quickly to guide emergency response efforts should an arboviral disease begin circulating on the island. At this time, the program has regained capacity to respond to multiple locations at once, employ various strategies as needed to abate mosquitoes, educate and allay fears of the public, and conduct surveillance to determine mosquito densities and efficacy of strategies.

Prevention

Although Hawai‘i is fortunate to be free from endemic arboviral diseases, vector species themselves are present year-round in many parts of the islands and can spread pathogens, such as dengue, upon importation. The program is strategically aiming to lessen future risks by suppressing mosquitoes through sanitation and larval source reduction (sanctioned effective methods to reduce mosquitoes^2–4) and mitigating exceptional opportunities for disease entry in the following ways.

First, routine surveillance and larval breeding source reduction have been restored at ports of entry to reduce the potential for establishment of new vectors in Hawai‘i. Vector Control staff have created a database listing sites capable of supporting mosquitoes. Subsequently, mosquitoes have either been permanently eliminated or mosquito suppression measures including regularly treating with larvacides to prevent mosquito development have been employed at those identified sites. Staff also conduct weekly trapping of mosquitoes to monitor population trends and identify immigrant species.

Next, areas hosting events that attract large crowds, especially with many international visitors, (eg, Ironman Triathlon, Kailua-Kona) are surveyed, and mosquitoes are suppressed in the weeks preceding the occasion in mid-October. The rationale for this strategy is to reduce the chance of contact between an infected individual arriving in Hawai‘i and mosquitoes that could potentially transmit the pathogen. In the example of the Ironman Triathlon, resorts and parks along the western coastal areas of the island spanning more than 75 miles are covered. For the same reason, scenic points and parks island-wide are regularly surveyed and mosquito suppression measures are implemented.

Vector Control routinely goes door-to-door within communities to educate the public and reduce mosquito breeding sites. Recognizing our limitations and need for community adoption of practices and behaviors that reduce mosquito populations and the risk of being bitten, this strategy is deemed valuable despite its labor intensity. Community interactions are mostly positive, and the program has begun to implement mechanisms to assess lasting impact of these activities. Side benefits of work in residential areas are that this activity creates familiarity with Vector Control program methods, allows some mosquito surveillance, and provides an opportunity to inventory habitat and artificial breeding sources, which can be used for future risk analysis or to determine the need for special community-based projects such as organized cleanups.

A final area of prevention activities is directed towards residential housing for the elderly as well as school areas, where human populations deemed potentially more vulnerable are concentrated.^5,6 As with previously described activities, staff regularly visit these areas and look for opportunities to disrupt mosquito development and assess mosquito population levels and species present.

Discernably the program has adopted a proactive approach through its emphasis and use of considerable resources on prevention detailed above. Activities are strategic, have clear goals, and assessment mechanisms are being implemented.

Response

Experiences during the 2015–16 dengue outbreak highlighted challenges and shortcomings of the singular approach to adult mosquito control implemented by the Vector Control program. That approach consisted exclusively of Aquareslin (permethrin + PBO, Bayer) applied with ultra-low volume backpack equipment (Hudson Porta-pak, HD Hudson Manufacturing). While the efficacy of both the product and approach is known,² there are some shortcomings. The strategy relies on tiny droplets (< 30microns) of pesticide solution drifting through the environment and contacting mosquitoes. This approach gains higher efficacy with relatively wide areas of applications but provides no residual control; can be impeded by dense vegetation; and is negatively influenced by weather events such as low humidity, wind, or air currents rising from the ground.² These factors, coupled with an intrinsic behavior of the mosquitoes to become less active and potentially sheltered in cryptic environments from mid-morning to late afternoon when most adulticide spraying occurred, led CDC to conclude there was an unknown capacity to control mosquitoes since some research has found applications outside of periods of activity may not be as effective.^1,7 CDC encouraged adoption of strategies to evaluate efficacy and develop methods to improve on knockdown of adult mosquitoes for greater periods of time. They also recommended adoption of a neighborhood scale approach rather than applications limited to a 25-yard radius surrounding residences with confirmed/suspected dengue cases. In their assessment, CDC also referenced the challenges in obtaining approval to treat properties and the lack of organic options as obstacles to overcome to improve the chemical control aspect of responding to disease outbreaks.¹ Since the outbreak, the Vector Control program has taken aggressive steps to overcome the challenges and address recommendations.

First the program has aligned itself with CDC recommendations on response, specifically using the “Zika CDC Interim Response Plan” and their “Surveillance and Control of Aedes aegypti and Aedes albopictus in the United States” as guidance. The program now both surveys and sprays wider focal areas (150 m radius), utilizes a range of products, adopts barrier or residual spraying where appropriate, and monitors the effect of interventions as well as resistant mosquito populations.^3,8 Activities are initiated when we are notified of a suspected arbovirus infected case.

Included among the new products are organic adulticides and larvacides that can be used on Organic Materials Review Institute (OMRI) certified organic farms as well as for homes opposed to traditional approaches. Also in inventory are products with a wider crop labelling to have capacity to apply treatments to fruit tree and food crops found on many properties. These options alone increase the overall treatment area and percentage of homes receiving mosquito abatement within target areas. Coverage of affected areas are often a predictor of mosquito population reduction.²

As mentioned earlier, the program has invested in new spray equipment. Among them are Stihl mistblowers (model SR450) designed to apply pesticides with a much coarser spray (500+ microns) and at much higher volumes. Mistblowers also have the capacity to achieve greater penetration into areas of dense foliage and cryptic environments. These types of applications are commonly known as either barrier or residual applications and have demonstrated efficacy.^9,10 Newly adopted mosquito surveillance activities following treatment in various habitat types have regularly found greater than 95% reduction in mosquito captures with control lasting more than two weeks. This approach overcomes several weaknesses identified during the 2015 outbreak. In most instances properties will not require a second application within a known case's period of viremia, which frees manpower to focus on newly identified cases or to extend the area of treatment around the case. Residual activity of the strategy reduces reliance on mosquito activity during the time of application as mosquitoes will continue to be killed days after the application as they rest on treated surfaces. Residents that decline treatment or are not at home during abatement activities will also gain some benefit since the spray strategy creates barriers to immigration and emigration of mosquitoes creating isolated populations. The barrier and residual strategies are also applied with traditional hand pumps to sides of buildings or other situations where drift is a concern and extends treatment right to people's doorways where peridomestic mosquitoes frequent and rest. In the past, efficacy was often limited in those types of locations because of a pesticide's interaction with construction material. To counter this effect the program has obtained a special polymer formulated product (Suspend Polyzone, deltamethrin, Bayer) to extend efficacy to concrete and rock surfaces.¹¹

Changes in response to disease introductions have been profound and are believed to substantially reduce risk to our residents as compared with the period prior to the dengue outbreak. Despite these and other positive actions in preparedness and prevention, the Vector Control program continues to strive for advances, recognizing the challenge and threat that introduced mosquito-borne diseases represent. We endeavor to keep the state free of arboviral diseases, contributing our share to realize the department's motto: “Healthy Communities, Healthy Islands, Healthy People.”